Data from: The effects of dietary macronutrients on flight ability, energetics, and fuel metabolism of yellow-rumped warblers Setophaga coronata

The catabolism of protein from organs and muscles during migratory flight
is necessary to produce glucose, key metabolic intermediates, and water,
but may have negative effects on flight range and refueling at stopovers.
We tested the hypothesis, suggested by previous studies, that birds that
eat high-protein insect diets use more protein for fuel in flight than
those that eat high-carbohydrate fruits. First, we fed migratory
yellow-rumped warblers synthetic fruit or mixed insect/fruit diets, and
measured metabolic rates and fuel mixture under basal conditions and
during exercise in a hop/hover wheel respirometer. Birds eating the fruit
diet had greater plasma triglyceride and non-esterified fatty acid
concentrations, and the higher protein mixed diet increased plasma uric
acid only during feeding. Diet did not affect metabolic rates or the fuel
mixture under resting or exercise conditions. We then fed yellow-rumped
warblers synthetic diets that differed only in the relative proportion of
carbohydrate and protein (60:15 versus 15:60 as % dry mass) and tested
them in wind tunnel flights lasting up to six hours. Birds fed the high
carbohydrate diet became heavier and fatter than when fed the high protein
diet. Plasma uric acid concentration was increased and plasma phospholipid
concentration was decreased by the high protein diet in the pre-flight
state (after a 3 h fast), but diet only affected plasma phospholipids
during flight (lower in high protein birds). Neither diet nor amount of
body fat affected the rate of loss of lean mass or fat during flight.
Inter-individual or seasonal differences in diet do not appear to
influence the amount of protein catabolized during endurance flight.
However, birds fed the high carbohydrate diet had greater voluntary flight
duration, independent of body fatness, suggesting that there may be other
performance benefits of high carbohydrate diets for migratory birds.